The lake Črno jezero in the mountain Pohorje is a reservoir (retainment of water previously used to bring the wood logs into the valley). The organic waste of dead plants and animals gathered on the bottom of this lake for years and eventually created a thick layer of dark, almost black ,silt. That is the reason that on your first look the lake looks full of ink despite the fact that the water is crystal clear. The lake itself looks remarkably similar to the bogs found in Finland.
The lake is home only to one endemic subspecie of brown trout -black with prominent red dots. The lake is situated in complete wilderness and you can access it only on foot- following the Slovenian mountain trail, approximately 15-20 min from the parking place.